PELECYPODA—PRIONODESMACEA. 



495 



marked with regular rays crossed by sharp concentric lamellae. 

 Hamilton : New York. 



363. L. tricostatus (Vanuxem). (Fig. 662, c, d.) Devonic. 

 Large ; beak pointed, not extending to margin of hinge. Rays 



of three sizes, crossed by fine concentric lines. 

 Lower and Middle Chemung of New York. 



XCVI. Crenipecten Hall. 

 Like Aviculopecten but with hinge line composed of a long row 

 of alternating teeth and sockets. Carbonic. 



364. C. winchelli Hall. (Fig. 663.) Mississippic-Carbonic. 

 Left valve moderately convex ; beak acute, prominent ; sur- 



Fjg. 663. Crenipecten winchelli. Left valve, and its upper portion enlarged to two 

 diameters. (Pal. N. Y., V. ) 



face with numerous rays. Right valve nearly flat ; beak obtuse, 

 depressed ; surface marked with obscure rays. 



Waverly : Ohio. Upper Coal Measures : Pennsylvania. 



XCVII. Pecten Muller. 



Nearly equilateral, very inequivalve, with well developed and 

 equal ears. One valve, usually the right, more convex than the 

 other. Surface usually marked with radial sculpture. Hinge 

 line straight, with a strong resiliifer, on each side of which inter- 

 locking ridges and grooves radiate in the adult. Byssal notch 

 always present in right valve, not very conspicuous. Single ad- 

 ductor muscle present. Carbonic— Recent. 



The genus Pecten has been divided into very many subgenera, 

 the most important of which are : Chlamys, Camptonectes, Ento- 

 liam, Syncyclonema, Amusium. Under each are here placed those 

 species which are most widely designated by these subgeneric 

 names. 



A. Surface of valves without radial ribs I. 



I. Interior of valves marked with small radial ribs I. 



1. Interior ribs 8 * 395. P. (Amusium) alabamensis. 



